The A6 is one of the main historic north-south roads in England. It currently runs from Luton in Bedfordshire to Carlisle in Cumbria, although it formerly started at a junction with the A1 at Barnet. It is the fourth longest numbered road in Britain, behind only the A1, A38 and A30.

South of Derby, the road is paralleled by the M1 motorway, between Manchester and Preston the M6 and M61 motorways approximate its course, and from Preston to its northern terminus in Carlisle it is paralleled by the M6 only. Between Derby and Manchester the A6 follows a completely different routing to the motorway network, crossing the Peak District rather than going around it. Because of these duplications, the A6 is less important than formerly.

The A6 begins as St Mary's Road at an elongated roundabout with the A505 road – part of the Luton inner ring road. The A6 follows Guildford Street – near the railway station – and into New Bedford Road. It meets the A5228 outer ring road at a roundabout. On the outskirts of Luton, now Barton Road, it meets the Icknield Way Path. Leaving Luton, it enters Central Bedfordshire after a roundabout with Quantock Rise.

There is a roundabout at Streatley, where the road becomes the dual-carriageway Luton Road, passing through the Bartonhill Cutting. The road becomes single carriageway at the roundabout with the B655 at the other end of the Barton-le-Clay bypass. It meets the A507 at a roundabout at Clophill, crossing the River Flit. It passes by Maulden Wood as the dual-carriage up Deadman's Hill then passes Haynes West End. It enters the district of Bedford and bypasses Wilstead. It meets the A421 at the Elstow Interchange grade-separated junction (GSJ). The A6 meets the A5134 at a large signal-controlled junction.

Kettering was bypassed when sections of the east-west corridor A14 were built. The road enters Leicestershire and the district of Harborough as Harborough Road at the start of the five-mile (8 km) Market Harborough Bypass. It briefly re-enters Northamptonshire again, and at this point there is a roundabout with the A427 (for Stoke Albany) and A4304 (former A427), and an exit for Great Bowden.

On the outskirts of Leicester the road becomes London Road. There is a roundabout with Florence Wragg Way, where the road becomes Glen Road It then becomes Leicester Road before reaching the outer ring-road (A563), next to Leicester Racecourse. It becomes London Road, where the dual-carriageway ends, and it enters the city of Leicester, passing the Leicester High School for Girls. There is a crossroads, for Stoughton Road (A6030) at Stoneygate, and a roundabout with the Victoria Park Road (B568). It passes close to Leicester University and many take-away shops. It crosses the Midland Main Line near Leicester railway station. In the centre of Leicester, it is subsumed into Leicester's inner ring-road, the A594.

Quorn-Mountsorrel bypass north of Leicester

It crosses the Grand Union Canal and the River Soar as St Margarets Way. It becomes dual-carriageway on the northern outskirts of Leicester, and passes the National Space Centre in Belgrave as Abbey Lane. Later, it meets a roundabout with the A563 outer ring-road entering the borough of Charnwood. North of Leicester, as Loughborough Road, it meets the A46 Leicester Western Bypass just south of Rothley and the start of the four-mile (6.4 km) dual-carriageway Quorn-Mountsorrel Bypass. The road at this point follows the Soar Valley, and is mostly on embankment or viaduct, crossing the river four times. From here the road goes through Loughborough. North of Hathern, there is a dual-carriageway section which skirts the Leicestershire–Nottinghamshire border (the River Soar). The road becomes London Road and enters the district of North West Leicestershire. It passes through Kegworth, and becomes Derby Road. It joins the M1 and A453 at the extremely busy roundabout of junction 24, which is where the A50 Derby to Stoke-on-Trent Link begins. The road follows one of the former A6 dual-carriageway sections, passing Lockington, before meeting traffic from the south-bound M1 at junction 24a. South-bound traffic on the A6 here has to negotiate a roundabout and a set of traffic lights, which has numerous and lengthy hold-ups at peak times. The three-laned A6 overlaps the A50 for a couple of miles, and there is a junction with the B6540 (former A453). The road crosses the Trent and Mersey Canal and River Trent, where it enters Derbyshire and the district of South Derbyshire.

Elvaston Castle is to the right. The road enters Derby initially along London Road, then at Alvaston it meets the A5111 Derby Ring Road ('Raynesway). It enters Crewton and just after a hump-backed bridge, it passes St Osmund's church. There is a roundabout with Ascot Drive near the Derby Conference Centre, and the road exits as Pride Parkway, which is related to the adjacent Pride Park Business Park and Pride Park Stadium, home of Derby County F.C.. It eventually reaches Litchurch near Derby College's new Roundhouse site; the land on which it was built was a former gas works. This section from the first roundabout to Station Approach (B6000) includes a 900-foot (270 m) viaduct, with 180-foot (55 m) spans, that crosses the Midland Main Line. The A6 meets a former route beside the new Westfield Derby, a former roundabout that was replaced with traffic lights with a multi-storey car park in the centre. The road overlaps the A601, Derby's inner ring-road and the A52, crossing the River Derwent, then leaving as King Street at an intersection on St Alkmund's Way near the former site of St Alkmund's Church. This section to the A38 has a weight limit. As Garden Street, it splits in two at an elongated roundabout surrounding the a service station and a pub. At a roundabout known locally as the Five Lamps, it becomes Duffield Road. North of Derby, there is the Palm Court roundabout (named after the former Palm Court café which closed in 2005), a junction with the A38. It follows the Derwent Valley, entering the district of Amber Valley through Duffield and Belper. At Whatstandwell it meets the B5035 (for Crich and Wirksworth), then enters the district of Derbyshire Dales. At Cromford, it meets the A5012 (Via Gellia). Entering Matlock, the road passes under the railway and along a new bypass and then over the River Derwent, meeting the A615 at a roundabout. The road then continues on Bakewell Road into Darley Dale, where the road, as Dale Road, passes the hospital, and crossroads with the B5057.

It then goes under the M60 near the junction with the M61, near the Worsley Braided Interchange and Wardley Hall (home of the Roman Catholic Bishop of Salford) and enters Whittle Brook and Walkden as Manchester Road, passing the Linnyshaw Industrial Estate on the right. The A6 meets the A575 (for Worsley and Farnworth) and B5232 (for Boothstown) at crossroads where the road is dual-carriageway as High Street. It becomes Manchester Road East and continues towards the district of Little Hulton. It meets the A5082 (for Tyldesley and Farnworth) at crossroads near St. Paul's, Peel, becoming Manchester Road West.

On leaving Little Hulton, the road enters the Borough of Bolton near the Chloride Battery Works. Near Farnworth, the road meets the M61, at junction 4, which closely follows parallel with the A6 up to Preston. The road is now the primary route Salford Road and meets the A579 at crossroads at Hulton Lane Ends becoming Manchester Road. It meets the A58 at a roundabout at Chequerbent and is no longer a trunk road. Close to M61 junction 5, the A6 enters Westhoughton. Then it crosses the Manchester to Southport railway line and meets the B5236 at Wingates, near the St. John's Primary School and the St. John the Evangelist Church. On leaving Westhoughton, the road becomes Chorley Road. At Four Gates, there is the B5239 for Aspull. It meets the A6027 roundabout close to the M61 junction 6 for Horwich. It passes through Hilton House, at Scot Lane End, it meets the B5408 for Blackrod, becoming the Blackrod By-Pass Road. It meets the B5238, for Horwich, at crossroads near Blackrod railway station. Close by on the M61 is the Rivington services (formerly Bolton West services). It rejoins the old route where it meets the B5408. It enters Adlington, and the district of Chorley where it crosses the River Douglas as Chorley Road, becoming Market Street. In the centre of Adlington it meets the B6227 near Adlington railway station, and the police station, becoming Church Street then Westhoughton Road. It crosses the Leeds and Liverpool Canal and meets the A673 from Bolton and A5106 from Standish.

It crosses the River Yarrow and passes the Albany Science College as Bolton Road. In Chorley, the central section is dual-carriageway with many roundabouts. It meets the B6228 at a roundabout, passes the railway station, then meets the A581 and B6229. It passes a hospital and meets the B5252 at a roundabout where it crosses the railway. The dual-carriageway A674 goes to Blackburn via the nearby junction 8 of the M61 and the Preston England Temple, a Mormon temple.

From Chorley, it meets the B6229 and B5248 at Whittle-le-Woods, passing the St John the Evangelist Church and crossing the River Lostock. It enters Clayton-le-Woods and meets the B5256 (for Leyland) at a roundabout near Cuerden Hall. It passes through Clayton Brook and crosses the M65, entering the district of South Ribble, near its western terminus. There are two roundabouts for the Walton Summit Industrial Estate, either of which lead to the Walton Summit Motorway. Next is a roundabout with the M6 at junction 29, which is now shared with the M65 where the it becomes a trunk road. The road becomes dual-carriageway as it enters Bamber Bridge. There are crossroads with the northern terminus of the A49 then a roundabout with the A582 – where the road heads north as London Way. The start of the M65 is accessible only from this roundabout at junction 1a. It crosses the East Lancashire Line and meets the B5257 at a roundabout. It meets the B6230 at a roundabout at Dog Kennel Wood, crosses the River Darwen and meets the A675 (for Walton-le-Dale).

Crossing the River Ribble south of Preston

It crosses the River Ribble and the Ribble Way, entering the district of Preston. The road enters Preston as a single carriageway, meeting the A59 (for Blackburn), B6243 (for Ribbleton), and A6063. It passes through the centre of Preston, becoming North Road, meeting the A5071 (Moor Lane), then becoming Garstang Road. The A6 passes Moor Park and crosses the A5085 Blackpool Road. At Fulwood, it meets the B6242 at crossroads, then passes Sharoe Green. It meets the B6241 Preston ring road near junction 1 of the M55.

It crosses Woodplumpton Brook and meets the B5269 at crossroads at Broughton. It meets Barton, still as Garstang Road, running along the Preston and Wyre district boundary. The A6 begins to run parallel to the West Coast Main Line, which it crosses. The district boundary crosses to the other side of the road and it enters the district of Wyre. It passes through Bilsborrow. It leaves the district boundary, and crosses the River Brock at Brock and passes over the Lancaster Canal. At Catterall, it meets the B6430 and crosses the River Wyre, and as Preston Lancaster New Road meets the A586 (for Churchtown). It enters Garstang and crosses the Lancaster Canal again. It meets the B5272 and B6430 and enters Cabus. At Forton, it passes close to the Forton service station on the M6. At Potters Brook, it meets a crossroads and enters the city of Lancaster. It meets the M6 at junction 33 and goes through Galgate as Main Road, passing under the West Coast Main Line, which it then runs adjacent to. The University of Lancaster lies in the 0.6-mile (1 km) separation between the A6 and the M6, where there is a short section of dual-carriageway on the A6 alongside the West Coast Main Line. The road enters Lancaster as Scotforth Road then Greaves Road.

It meets the A588 Ashton Road for Preesall at a roundabout, goes past the Royal Lancaster Infirmary on the left, then crosses the Lancaster Canal. It splits up in two as it passes through the centre of Lancaster. It rejoins and splits again to cross the River Lune on the Greyhound Bridge and older Skerton Bridge. The A589 leaves for Morecambe and the A683 leaves for Caton and M6 junction 34. The road rejoins as Owen Road near Skerton Community High School and there is the B5231 for Morecambe, and a road for Halton. It crosses the Lancaster Canal and heads through Hest Bank as Lancaster Road passing Bolton Town. It crosses the Lancaster Canal and meets the A5105 Coastal Road (from Morecambe) to the left at Bolton-le-Sands. Here the road is at its closest point to Morecambe Bay. It follows the Lancaster Canal and enters Carnforth as Lancaster Road, and meets the B6254 which leads to M6 junction 35.

It climbs up to over 1,400 feet (430 m) and heads over the Shap Fells into Wasdale, where it leaves the National Park, and passes the RMC granite works. A spur of the A6 meets the B6261 and joins the M6 at junction 39. The road is no longer a trunk road and passes the CorusLime Kilns on Hardendale Fell and enters Shap where it is crossed by the Coast to Coast Walk, and over the West Coast Line. It passes under then over the M6, then passes close to Hackthorpe Hall and the Lowther Castle Inn. It passes over the M6 near Lowther, which is near the Lakeland Bird of Prey Centre. It passes over the railway at Clifton near Penrith. There is a turn for Brougham and it crosses the River Lowther at Eamont Bridge where it meets the B6262 and crosses the River Eamont over a narrow bridge. It meets the A66 at Kemplay roundabout next to Penrith Hospital.

The Roman road section south of Carlisle

The A6 takes a central route through Penrith, entering the town as Bridge Lane then Victoria Road and leaving as 'Stricklandgate then Scotland Road. North of Penrith, it meets the B5305 (which heads to Wigton) at the Stoneybeck roundabout situated on a new section of the A6 built for junction 41 of the M6. The next section of the A6 is one of the most dangerous roads in the county and follows a former Roman road, having seen several deaths in the past few years.[1][2]

This section through Inglewood Forest essentially follows a parallel path to the M6, and passes through Plumpton where it meets the B6413; an old Roman fort called Voreda at Castlesteads; High Hesket which it bypasses; Low Hesket; enters the district of Carlisle near Cotehill; and meets the M6 (and the B6263) eventually at junction 42: the start of the Carlisle bypass. Entering Carlisle, it crosses the River Petteril (near a large radio mast) then the Tyne Valley railway line. The A6 travels through south-eastern Carlisle as London Road, before finishing at Botchergate in the centre of Carlisle where it transforms seamlessly into the A7 which runs out of Carlisle and across the Anglo-Scottish border terminating eventually at Scotland's capital city of Edinburgh.

The route of the old A6 south of Luton is now the A1081 for most of its length. In the initial road numbering scheme, the A6 started in Barnet where it joined what was then the A1Great North Road. From Barnet the road went to London Colney, St Albans, Harpenden to join the current start of the road at Luton. At St Albans, the road met the then A5 at a crossroads: going north on both roads, the A5 arriving from the southwest, and leaving the crossroads northwest, and the A6 arriving from the southeast and leaving to the northeast. Nowadays that stretch of the A5 has also been renumbered so that the crossroads in St Albans is now A5183 and A1081.

Nelstrop Road North, which runs adjacent to Houldsworth Golf Club, approximately half a mile (800 m) east of Levenshulme, was originally a stretch of the A6 before it was moved westwards to its current route. Being on the border of two districts, the road has fallen into a state of disrepair as neither the City of Manchester nor the Metropolitan Borough of Stockport claims responsibility for it.[citation needed]